1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for use in oil and gas wellbores. More particularly, the invention relates to methods and apparatus for utilizing deployment valves in wellbores.
2. Description of the Related Art
Oil and gas wells typically begin by drilling a borehole in the earth to some predetermined depth adjacent a hydrocarbon-bearing formation. After the borehole is drilled to a certain depth, steel tubing or casing is typically inserted in the borehole to form a wellbore, and an annular area between the tubing and the earth is filed with cement. The tubing strengthens the borehole, and the cement helps to isolate areas of the wellbore during hydrocarbon production.
Wells drilled in an “overbalanced” condition with the wellbore filled with fluid or mud preventing the inflow of hydrocarbons until the well is completed provide a safe way to operate since the overbalanced condition prevents blow outs and keeps the well controlled. Overbalanced wells may still include a blow out preventer in case of a pressure surge. Disadvantages of operating in the overbalanced condition include expense of the mud and damage to formations if the column of mud becomes so heavy that the mud enters the formations. Therefore, underbalanced or near underbalanced drilling may be employed to avoid problems of overbalanced drilling and encourage the inflow of hydrocarbons into the wellbore. In underbalanced drilling, any wellbore fluid such as nitrogen gas is at a pressure lower than the natural pressure of formation fluids. Since underbalanced well conditions can cause a blow out, underbalanced wells must be drilled through some type of pressure device such as a rotating drilling head at the surface of the well. The drilling head permits a tubular drill string to be rotated and lowered therethrough while retaining a pressure seal around the drill string.
A downhole deployment valve (DDV) located within the casing and operated through a control line may be used to temporarily isolate a formation pressure below the DDV such that a tool string may be quickly and safely tripped into a portion of the wellbore above the DDV that is temporarily relieved to atmospheric pressure. An example of a DDV is described in U.S. Pat. No. 6,209,663, which is incorporated by reference herein in its entirety. Thus, the DDV allows the tool string to be tripped into the wellbore at a faster rate than snubbing the tool string in under pressure. Since the pressure above the DDV is relieved, the tool string can trip into the wellbore without wellbore pressure acting to push the tool string out. Further, the DDV permits insertion of a tool string into the wellbore that cannot otherwise be inserted due to the shape, diameter and/or length of the tool string.
An object accidentally dropped onto the DDV that is closed during tripping of the tool string presents a potential dangerous condition. The object may be a complete bottom hole assembly (BHA), a drill pipe, a tool, etc. that free falls through the wellbore from the location where the object was dropped until hitting the DDV. Thus, the object may damage the DDV due to the weight and speed of the object upon reaching the DDV, thereby permitting the stored energy of the pressure below the DDV to bypass the DDV and either eject the dropped object from the wellbore or create a dangerous pressure increase or blow out at the surface. A failsafe operation in the event of a dropped object may be required to account for a significant amount of energy due to the large energy that can be generated by, for example, a 25,000 pound BHA falling 10,000 feet in air.
Increasing safety when utilizing the DDV permits an increase in the amount of formation pressure that operators can safely isolate below the DDV. Further, increased safety when utilizing the DDV may be necessary to comply with industry requirements or regulations such as standards that require a double barrier or redundant seals between the isolated formation pressure below the DDV and operators at the surface.
Therefore, there exists a need for apparatus and methods that provide a fail safe operation when utilizing a DDV. There exists a further need for apparatus and methods that permit a DDV to maintain a closed position or at least a safe operating position in the event of a dropped object.